The present invention relates to opacity measuring devices and, in particular, to an opacity measuring apparatus and method of obtaining an accurate density (opacity) measurement of the effluent flowing through a furnace stack over relatively long periods of time.
Many systems found in the prior art are designed to measure the density of effluent emanating from furnance stacks. This measurement has become increasingly important of late, since the general public, as well as, environmentalists are concerned with pollution of the atmosphere by waste products obtained by various chemical and sundry product manufacturing processes. These waste products or effluents are frequently expelled via a furnace stack into the atmosphere to be dispersed by air currents. However, the effluents frequently linger on in one place contaminating the air, thereby causing a health hazard to all living things.
The prior art systems of which I am aware approach the problem of obtaining accurate density measurements of effluents emanating from furnace stacks in many ways; each striving to obtain accurate measurements with a simple system requiring a minimum of time and expense for their adjustment and calibration. These systems frequently use a reflective system in which both a measuring light flux, reflected from a reflex-reflector or mirror at the end of a measuring distance and a reference light flux from the original light source are directed onto a photoelectric detector, as disclosed in U.S. Pat. Nos. 3,857,641 to Gass and 3,796,887 to Vincent et al. Other systems utilize a pair of photocells (photoelectric detectors) to accomplish a similar result, as disclosed in U.S. Pat. Nos. 3,838,925 to Marks; 3,743,430 to Riggs and 3,690,774 to Kottle et al. Still another system for measuring the opacity of an effluent utilizes a pair of light sources for this measurement, as disclosed in U.S. Pat. Nos. 3,850,529 to Brugger. Some of the above identified patents, in addition, utilize a light pipe to provide an alternate light path for the collimated light source which is used as a measurement reference. However, to the best of my knowledge, none of the systems disclosed to date, have been able to meet all the requirements of the Environmental Protection Agency for Emission Monitoring as set forth in Part V of the Federal Register, dated Monday, Oct. 6, 1975.
The instant invention overcomes the shortcomings found in the prior art by providing an opacity measuring apparatus which utilizes a single collimated light source, a single photoelectric detector, a light pipe external to the stack providing alternative light paths to yield a reference signal and a correction signal for the output signal, which maintains the required accuracy.
Therefore, it is an object of the present invention to provide a relatively inexpensive accurate apparatus to measure the opacity of effluents flowing through furnace stacks.
Another object of the present invention is to provide an opacity measuring apparatus which is capable of being automatically and continuously calibrated.
A further object of the present invention is to provide an opacity measuring apparatus which may be easily installed and aligned with minimum time and effort.
A still further object of the present invention is to provide an opacity measuring apparatus which is capable of meeting all the requirements set forth by the Environmental Protection Agency.
Another object of the present invention is to provide an apparatus which requires minimum maintenance, and when required, may be readily performed.